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Biomedical subjects

M J Harrison

Publications and source records attributed to M J Harrison.

At least 181 records · Page 10Linked to original sources
PubMed1989

The cubic growth of AIDS cases: general dependence on early infection rates and distribution of times to appearance of clinical symptoms.

An observed cubic dependence on time of the cumulative growth in numbers of AIDS patients is shown to be the leading term of a power series in general. The cubic leading term follows from a nearly model-independent description of the rate of HIV infection, provided only that there is a distribution of incubation times to the appearance of clinically diagnosed AIDS symptoms with a finite initial derivative, that none of those infected exhibit immediate indications of illness, and that the epidemic begins with a finite initial rate of infection.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Impairment of cerebral function following cardiac and other major surgery.

Patients undergoing routine coronary artery surgery (N = 76) were compared with those undergoing other major operations (N = 29) in a prospective multidisciplinary study designed to define the incidence of neurological and psychological sequelae. The preoperative state of the carotid and vertebral arteries was defined by digital subtraction angiography. Changes in clinical neurological examination, detailed neuropsychological testing, psychiatric assessment and cerebral blood flow were measured. All preoperative studies were repeated 8 days and 8 weeks after surgery. Clinical neurological examination was repeated in addition on the 1st postoperative day. New focal neurological signs were found in 8% of the cardiac patients and none of the comparison group 24 h after operation (P = 0.9). Global transient neurological dysfunction occurred in 59% of the coronary group in the 1st postoperative day compared with 21% in other forms of surgery (P = 0.0007) but this correlated with postoperative narcotic and sedative drugs. A deterioration in neuropsychological performance was detectable in 73% of coronary cases at 8 days which was more likely to occur with increasing age, longer bypass time and lower perfusion pressure, but similar neuropsychological changes also occurred in 50% of the comparison group. By 8 weeks, there was a significant improvement in the cardiac patients (37%, P less than 0.001) but not in the other group. Cerebral blood flow was reduced at 8 days in the coronary bypass patients but not in the comparison group suggesting that the mechanism of cerebral change may be different in the two groups.

Adult↗
PubMed1989

Retinal microembolism and neuropsychological deficit following clinical cardiopulmonary bypass: comparison of a membrane and a bubble oxygenator. A preliminary communication.

To observe and quantify cerebrovascular microembolic events in the central nervous system during cardiopulmonary bypass, 40 patients having elective uncomplicated coronary surgery had retinal fluorescein angiograms 5 min before bypass was discontinued. Each patient also had 10 neuropsychological tests before and after surgery. A Harvey H1700 bubble oxygenator was used for 23 patients and a Cobe CML sheet membrane oxygenator was used for 17 patients. All 23 (100%) of patients in the bubble oxygenator group had retinal microvascular occlusions consistent with microembolism compared to 8/17 (47%) in the membrane oxygenator group (P less than 0.001). In those retinas with occlusions, the mean resultant area of non-perfusion was less in the membrane oxygenator group (0.11 mm2; n = 8) than in the bubble oxygenator group (0.29 mm2; P less than 0.01). Arterial PO2 levels during bypass were similar in both groups at moderate hypothermia, but the mean PaO2 during rewarming was higher in the bubble oxygenator group (27 kPa) than in the membrane group (13 kPa; P less than 0.001). Neuropsychological deficits were more common and more severe after bubble oxygenation than after membrane oxygenation, but in this small patient group, the difference was not statistically significant. We conclude that flat sheet membrane oxygenation during cardiopulmonary bypass may confer significant protection against cerebrovascular microembolism.

Cardiopulmonary Bypass↗
PubMed1989

Effect of bezafibrate on the sequelae of acute experimental focal cerebral ischaemia.

The possibility that the ability of bezafibrate to lower the oxygen affinity of haemoglobin might lead to an increased oxygen delivery to ischaemic cerebral tissue was explored in preliminary studies in two animal models. The combined morbidity and mortality of unilateral carotid ligation in the gerbil appeared to be reduced at two hours in bezafibrate treated animals. By four hours and thereafter the outcome was unaffected. Two hours after MCA occlusion bezafibrate-treated rats showed a significantly reduced rise in tissue lactate concentration (p less than 0.01) suggesting less anaerobic metabolism had occurred in the ischaemic tissue.

Acute Disease↗
PubMed1989

Do leukocytes have a role in the cerebral no-reflow phenomenon?

The possible role of leukocytes in the cerebral microcirculation following ischaemia was assessed in the gerbil. The no-reflow phenomenon seen after 30 minutes of severe bilateral hemispheric ischaemia during hypotensive reperfusion was compared in control animals and in a group made leukopenic by pretreatment with cyclophosphamide. Neither the incidence nor the severity of the no-reflow phenomenon differed between the two groups. The evidence from this study casts doubt on the hypothesis that leukocyte plugging plays a major role in the cerebral microcirculation's response to ischaemia.

Animals↗
PubMed1989

Subclinical neurological and neuropsychological effect of infection with HIV.

Thirty one homosexual men with antibody to human immunodeficiency virus (HIV) but without major neurological complaints were assessed in a cross sectional study of neurological and neuropsychological function. Eleven patients had AIDS, 10 had persistent generalised lymphadenopathy (PGL), and 10 had HIV infection without PGL (called "well"). Thirteen age matched homosexual men without antibody to HIV acted as controls. Significant abnormalities were found in six on clinical neurological examination, in eight on nerve conduction studies, in six on electroencephalography, in six on neuropsychological assessment, and in eight on computed tomography of the head. Eighteen patients (nine with AIDS, four with PGL, and five "well") performed abnormally in at least one section of the assessment. The study highlights the incidence of nervous system dysfunction in HIV infection even in people who do not have AIDS. Prospective evaluation using electrophysiological and imaging techniques is necessary to assess the natural history of such manifestations and the effect of antiviral treatment.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Sex difference in antithrombotic effect of aspirin.

A number of clinical trials suggest that the antithrombotic effect of aspirin is limited to men. To test the possibility that this is due to a sex difference in the inhibitory effect of aspirin on platelet behavior, we studied whole-blood platelet aggregation in men and women and in male patients with carcinoma of the prostate receiving hormone therapy. The in vitro inhibitory effect of aspirin on so-called spontaneous platelet aggregation induced by stirring whole blood and monitored by the decrease in the number of singleton platelets was greater in men (mean +/- SD inhibitory ratio 1.54 +/- 0.30 in men, 1.23 +/- 0.22 in women; p less than 0.001). The inhibitory effect of aspirin was reduced in orchiectomized male patients and was restored by the addition of testosterone to blood samples. Estradiol had no detectable influence on the inhibitory effect of aspirin. Testosterone thus seems to influence platelet aggregation and its inhibition by aspirin as assessed by whole-blood in vitro aggregometry. Possible mechanisms for this effect of testosterone and its relevance to the choice of antithrombotic therapy are discussed.

Adult↗
PubMed1989

Arterial disease risk factors and angiographic evidence of atheroma of the carotid artery.

We conducted a prospective study of serial intravenous digital subtraction angiography to determine the relation of arterial disease risk factors and hemostatic variables with the presence of visible atheroma at the carotid bifurcation. Of the 492 patients with cerebrovascular disease or ischemic heart disease who entered the study, 354 had hematologic studies, including platelet aggregation in 230. Abnormal angiograms were associated with greater age, treated hypertension, current smoking, and lower hemoglobin levels but with higher uric acid, factor VIII, and fibrinogen concentrations. In patients presenting with isolated transient ischemic attacks, abnormal angiograms were also associated with higher levels of cholesterol and triglycerides. To study atheroma progression, the 230 patients with complete data at entry were recalled 2 years later. Repeat angiography in 209 patients showed progression of visible bifurcation disease in 13.4%. There was some evidence that progression was linked to higher age, hypertension, and more severe disease at entry, but further analysis was hampered by the small number of patients showing increased plaque size. The possible role of risk factors and hemostatic variables, especially fibrinogen, is discussed. Factors that did not correlate with progression of angiographically visible disease may also influence clinical end points by other mechanisms, such as thrombogenesis.

Aging↗
PubMed1989

Cerebrovascular disease and functional outcome after coronary artery bypass surgery.

A series of patients undergoing coronary artery bypass surgery was studied prospectively to see if angiographic evidence of cerebrovascular disease proved predictive of the incidence of neuropsychological deficit 8 days or 8 weeks after surgery. In 47 patients, intravenous digital subtraction angiography was carried out preoperatively to assess the presence and severity of atheromatous changes in the carotid arteries; 51% had evidence of vessel wall disease and 17% had stenosis of at least one carotid artery in the neck, although only one patient had severe narrowing. Overall, 77% of these 47 patients showed a neuropsychological deficit as defined by a significantly reduced score in at least two of 10 tests administered 8 days after surgery. Eight weeks after surgery 36% still showed a deficit. The incidence of neuropsychological deficit was not significantly greater among those patients with angiographically visible carotid artery disease. The mechanism of surgery-related cognitive impairment is briefly discussed in the light of these findings.

Brain↗
PubMed1989

Influence of haematocrit in the cerebral circulation.

Cerebral blood flow is inversely related to in vitro whole blood viscosity, the major determinant of which is haematocrit. Haemodilution increases cerebral blood flow in polycythaemic patients and in subjects with high normal haematocrit. There is now increasing evidence that this relationship reflects a homeostatic and physiological regulation of oxygen-carrying capacity. A high normal haematocrit proves to be a weak risk factor for stroke whilst stroke risk is clearly related to the target haematocrit in patients treated for polycythaemia rubra vera. Whilst venesection remains accepted prophylactic treatment against stroke and other vaso-occlusive events in the latter case, no large scale trial has formally assessed the role of haematocrit reduction in patients with early manifestations of cerebrovascular disease like transient ischaemic attacks or in the early stages of multi-infarct dementia. There are theoretical reasons why a high haematocrit might have adverse effects on the cerebral circulation in the presence of vessel occlusion. Thus, flow and therefore oxygen delivery would become constrained by high viscosity (haematocrit) in the maximally dilated ischaemic vascular bed, and secondary thrombosis would be encouraged by low flow rates, and increased cell-cell interaction. These arguments have led to two large multicentre clinical trials of haemodilution in acute stroke victims. Neither has revealed any clinical benefit in the treated group. The reasons for the failure of the trials are discussed. It is envisaged that haemodilution, as well as retaining a clinical role in the prevention of stroke in patients with polycythaemia, may be used as an adjunct to other therapy for the immediate sequelae of cerebral ischaemia.

Cerebrovascular Circulation↗
PubMed1988

The combined effects of hypertension, hemodilution, and osmotherapy on the metabolic sequelae of acute experimental cerebral ischemia.

The effects of induced hypertension, hemodilution, and osmotherapy (mannitol) have been assessed singly and in combination on the metabolic sequelae 2 hr after middle cerebral artery (MCA) occlusion in the anesthetized rat. All regimes that included hypertension and monotherapy with mannitol significantly reduced the rise in hemispheric lactate produced by vessel occlusion. No treatment caused increase cerebral edema, and mannitol produced a slight reduction in the hemisphere water content. The significance of the results is discussed.

Animals↗
PubMed1988

Peripheral neuropathy complicating pancreatitis and major pancreatic surgery.

Four cases of a polyneuropathy associated with pancreatitis and pancreatic pseudocyst formation are reported. Electrophysiological investigation showed the peripheral neuropathy to be predominantly axonal in type. These patients were all seriously ill and many factors may have been involved in the pathogenesis of their neuropathy. They had all received parenteral nutrition and multiple drug therapy including metronidazole, and all had severe sepsis. There was evidence that insufficient vitamin replacement had been given during total parenteral nutrition. It was not possible to decide whether the polyneuropathy resulted from the summation of these factors, is similar to what has been called the polyneuropathy of the critically ill, or is a new association with pancreatic disease.

Acute Disease↗